Going through some threads, I came across quite a few instances of incomplete/incorrect tags which hinder one's reading, so I thought maybe a thread listing the syntax of all the existing tags would be a handy resource. Anyway, here goes:

The basic formatting tags

The Bold tag:
Syntax: Text that should appear in bold.

The Italics tag:
Syntax: Text that should appear in italics.

The Underline tag:
Syntax: Text that should appear underlined.


Fonts, sizes, and colours

To change the font:
Syntax: [ FONT=font_name ]Text which appears in special font.[/FONT]
For font_name, replace the name of the font to be used. (eg. Arial) Be sure to use only those "system fonts" which everybody is sure to have.

To change the font size:
Syntax: Text which appears in a different font size.
For x, replace an integer between 1 and 7.

To change the font colour:
Syntax: Text that appears in a separate colour.
For colour, you could replace any one of the common colours (eg. Red, Black, DarkRed etc.). For more options see the advanced reply section.


Text Alignment

To align text to the left:
Syntax: Text that is to be left-aligned.

To align text to the right:
Syntax: Text that is to be right-aligned.

To center text:
Syntax: Text that is to be centered.


Inserting links and images

Inserting hyperlinks:
Syntax: [ URL=url_of_resource]The text link.[/URL]
For url_of_resource, replace the complete web (not local!!) url of the file you're linking to.

Inserting images:
Syntax: img_url
For img_url, replace the complete web url of the image you want to display.

Note: Make sure you adhere to the rules while posting links and images.


Some additional tags 'n tips

The quote tag:
Syntax: [ QUOTE=speaker]What the speaker said.[/QUOTE]

For speaker, replace the name of the person whose words you're quoting.

The subscript tag:
Syntax: Text that appears as subscript.

The superscript tag:
Syntax: Text that appears as superscript.

Use the subscript and superscript tags to post accurate chemical formulae. It not only looks better, but it also reduces the chances of someone misreading complex forulae, too.

To state temperatures, use:
xx.x o C / F


Note: To ensure that the software didn't interpret the demonstrations as actual tags, I had to include a space before the closing bracket of the tags. This space should be omitted when actually using the tags.

An easier way to make the degree symbol, as relates to angles and temperatures, is to use "& #186;". (No quotes or space)

& #186;F translates into ºF

Neat, huh? Amazing what extended character codes can do for you.

You can also use hexidecimal color codes, rather then "Red" or such, in your font tag.

BTW, nice to see a newbie do something useful for a change. :)

And while all these options give a person awesome capabilites, so too must that power be tempered by the wisdom in knowing when NOT to use it.

People who turn their posts in to kalidescopic displays of the color spectrum will soon disappear like a rainbow on a sunny day. ;)

Same too with varying font sizes, differing type fonts, etc.

Use the power wisely, or the dark side will squash you! :D

That alt trick to print extended ascii characters doesn't work for me, for some reason... Every time I insert a special character, when I preview the message, a different special character shows up!

http://www.cloford.com/resources/charcodes/symbols.htm

Which characters are displayed depends on the character set your computer is using, which varies with your O/S and region.